Ethylene trimerization

ABSTRACT

Ethylene is trimerized to form 1-hexene by using a catalyst comprising an aluminoxane and polydentate phosphine, arsine, and/or stibine coordination complex of a chromium salt. Catalysts, complexes, and ligands enabling production of 1-hexene in extremely high yields and purity are also described.

REFERENCE TO RELATED APPLICATIONS

This is a divisional of U.S. application Ser. No. 08/519,277, filed Aug.25, 1995, now U.S. Pat. No. 5,815,618; which is a CIP of Ser. No.08/227,433 filed Apr. 14, 1994, now U.S. Pat. No. 5,550,305; which is aCIP of Ser. No. 08/025,524, filed Mar. 3, 1993, now abandoned; which isa CIP of Ser. No. 07/914,489, filed Jul. 14, 1992, now U.S. Pat. No.5,744,677; which is a continuation of Ser. No. 07/777,137, filed Oct.16, 1991, now abandoned.

TECHNICAL FIELD

This invention relates generally to the oligomerization of ethylene andmore specifically to the preparation of 1-hexene by the trimerization ofethylene using a catalyst which includes an aluminoxane and a chromiumcomplex containing a coordinating polydentate phosphine, stibine orarsine ligand, such as a tridentate phosphine complex of a chromiumsalt.

BACKGROUND

My copending U.S. application Ser. No. 07/914,489, whose teachings areincorporated herein by reference, discloses an ethyleneoligomeriiation/trimerization process which uses a catalyst comprising achromium complex which contains a coordinating polydentate ligand and analuminoxane to produce high quality α-olefins which are enriched in1-hexene. Suitable ligands include cyclic polyamines, and polypyrazolylborates.

In my copending U.S. application Ser. No. 08/227,433 (which incorporatestherein the disclosure of U.S. Ser. No. 08/025,524), I have shown thatcertain polydentate ligand complexes of chromium salts in combinationwith aluminoxanes can catalyze ethylene oligomerization, and especiallyethylene trimerization to form 1-hexene with a very high degree ofselectivity, e.g. about 96%, with formation of product containing lessthan 2 wt % of polyethylene. The disclosure of my copending U.S.application Ser. No. 08/227,433 is incorporated herein by reference.

Prior art ethylene trimerization processes, such as are described inU.S. Pat. Nos. 4,668,838 and 4,777,315 which use mixtures of a chromiumcompound, an aluminoxane and a third component selected from hydrocarbylisonitriles, amines and ethers, are reported to produce amounts ofpolyethylene ranging from about 18 to 90+ percent as a coproduct. Suchpolyethylene not only decreases the yield of desirable product but alsocauses problems due to polymer build-up which would be expected tohamper the commercial use of such processes.

THE INVENTION

In sharp contrast to the results shown in U.S. Pat. Nos. 4,668,838 and4,777,315, the present invention provides a process and catalyst systemswhich can readily avoid the coproduction of significant amounts ofpolyethylene (less than about 2.0 wt % and normally from 0 to 1.5 wt %)with most of the byproducts being useful short chain olefins,particularly 1-butene. Moreover, this invention enables the productionof a hexene product of such high purity (e.g., 98 to 99% 1-hexene) that,for most commercial applications, the trouble and expense of furtherpurification of the hexene fraction is not required. In other words, theinvention makes it possible to form 1-hexene directly, while at the sametime avoiding undesirable isomerization of the product to internalolefin isomers.

Moreover, it has been found possible to form high purity 1-hexeneproduct with a catalyst productivity rate equivalent to as much as14,000 parts by weight of product per part by weight of chromiumcompound used in the catalyst. The productivity of the catalysts of theabove-mentioned prior art processes are limited by polyethyleneformation to the range of about 500 to 1,000 g hexene/g chromiumcompound.

One aspect of this invention is the discovery of a new type of ligandswhich, when complexed with a chromium compound, provides a catalystcomponent exhibiting extremely high 1-hexene selectivity and yield whenused in conjunction with an aluminoxane. These ligands are asymmetricalpolydentate phosphines, arsines and stibines having the formula:##STR1## where Z, which can be the same or different, is phosphorus,arsenic or antimony, (and preferably all three of them are phosphorusatoms), R is a hydrocarbyl group, R¹ is a dimethylene group and R² is alinear polymethylene group having at least 3 carbon atoms, e.g., 3 toabout 20 carbon atoms, preferably 3 to 6 carbon atoms, and mostpreferably a trimethylene group (--CH₂ CH₂ CH₂ --). The makeup of Rappears relatively unimportant as it can be alkyl, cycloalkyl, alkenyl,cycloalkenyl, aryl, aralkyl, etc. Typically, R will contain no more thanabout 12 carbon atoms, although theoretically there is no apparentreason why the hydrocarbyl group may not contain even more carbon atoms,provided the group does not sterically encumber the non-terminal Z atomto which it is attached to such an extent as to prevent the compoundfrom forming a tridendate complex with a chromium compound. On the otherhand, the makeup of the groups attached to the terminal Z atoms has aprofound effect upon the excellence of the results that can be achievedby the practice of this invention. For example, experiments conducted todate with asymmetrical tridentate ligands indicate that use of analuminoxane-chromium complex catalyst formed, for example, from atridentate compound of the formula ##STR2## where R, R¹, R² and Z are asdefined above, but where the terminal Z atoms are substituted by ethylgroups, may not be capable of forming an effective trimerizationcatalyst. In contrast, results from a catalyst derived from a similarasymmetrical tridentate compound of formula (1) above where there aremethyl substituents on the terminal Z atoms, not only consistentlyformed trimerization product with less than 2 wt % of polyethylene, butgave much faster reaction rates, higher hexene yields, and lowerinternal hexene isomer formation.

The foregoing asymmetrical polydentate compounds of this invention canbe formed by a two step synthesis process which comprises reacting amonohydrocarbyl phosphine, arsine or stibine with amono(ω-alkenyl)dimethyl phosphine, arsine or stibine of the formula

    R.sup.3 --Z(--CH.sub.3).sub.2

to form a disubstituted bidentate compound of the formula ##STR3## whereZ, R and R² arm defined above and R³ is a linear ω-alkenyl group havingat least 3 carbon atoms, and then reacting this bidentate compound withdimethylvinyl phosphine to form a compound of formula (I) above. Thesereactions are conducted under radical-initiated addition conditionsunder a dry, inert atmosphere.

In accordance with another embodiment of this invention, there isprovided a process for the trimerization of ethylene which processcomprises reacting ethylene using a catalyst comprising an aluminoxaneand a polydentate phosphine, arsine and/or stibine coordination complexof a chromium salt so as to form 1-hexene.

In a particular embodiment of this invention, this process is conductedusing a polydentate phosphine, arsine and/or stibine coordinationcomplex of a chromium salt formed from an asymmetrical polydentatephosphine, arsine and/or stibine of formula (I) above, most preferablywhere each Z is phosphorus.

Also provided is an ethylene trimerization catalyst compositioncomprising an aluminoxane and a polydentate phosphine, arsine and/orstibine coordination complex of a chromium salt.

Another particular embodiment of this invention involves conducting thisprocess using a polydentate phosphine, arsine and/or stibinecoordination complex of a chromium salt formed from an asymmetricalpolydentate phosphine, arsine or stibine of formula (I) above, mostpreferably where Z is phosphorus.

Still another embodiment is a group of novel and eminently usefulcoordination complexes of a chromium salt and a polydentate phosphine,arsine and/or stibine coordination complex of a chromium salt formedfrom an asymmetrical polydentate phosphine, arsine or stibine of formula(I) above, most preferably where Z is phosphorus.

These and other embodiments will become still further apparent from theensuing description and appended claims.

Aluminoxanes for use in the process of the invention can be prepared asknown in the art by reacting water or water-containing materials withtrialkylaluminum compounds in proportions of from about 0.5 to 1.2equivalents of water and, preferably, 0.8 to 1.0 equivalents of waterper equivalent of trialkylaluminum. For example, Manyik et al., U.S.Pat. No. 3,300,458, prepare alkylaluminoxane by passing a hydrocarbonsolvent through water to form a wet hydrocarbon solvent and mixing thewet hydrocarbon solvent with an allyl aluminum/hydrocarbon solventmixture in a conduit.

Schoenthal et al., U.S. Pat. No. 4,730,071, show the preparation ofmethylaluminoxane by dispersing water in toluene using an ultrasonicbath and then adding a toluene solution of trimethyl aluminum to thedispersion. Schoenthal et al., U.S. Pat. No. 4,730,072 is similar exceptit uses a high speed, high shear-inducing impeller to form the waterdispersion.

Edward et al., U.S. Pat. No. 4,772,736, describe an aluminoxane processin which water is introduced below the surface of a solution ofhydrocarbyl aluminum adjacent to a stirrer which serves to immediatelydisperse the water in the hydrocarbon solution.

The preparation of alkyl aluminoxanes from R₂ AlOLi formed by reactingAIR₃ and anhydrous lithium hydroxide, and R₂ AlCl has been reported inthe literature, for example, Ueyama et al., Inorganic Chemistry, 12, No.10, 2218 (1973) and Aoyazi et al., Inorganic Chemistry, 12, No. 11, 2702(1973).

Sinn et al., U.S. Pat. No. 4,404,344 prepare methylaluminoxane by addingtrimethyl aluminum to a slurry of CuSO₄ •5H₂ O in toluene. Introducingwater as a metal hydrate controls its reactivity with the trimethylaluminum. Kaminsky et al., U.S. Pat. No. 4,544,762, is similar except ituses an aluminum sulfate salt hydrate to supply the water. Likewise,Welborn et al., U.S. Pat. No. 4,665,208, describe the use of other metalsalt hydrates such as FeSO₄ •7H₂ O as a water source in preparingaluminoxane.

Hydrocarbylaluminoxanes may exist in the form of linear or cyclicpolymers with the simplest compounds being a tetraalkylaluminoxane suchas tetraethylaluminoxane, (C₂ H₅)₂ AlOAl(C₂ H₅)₂. Preferred aluminoxanesare prepared from triaikyl aluminum compounds such as triethyl aluminum,tri-n-butyl aluminum, triisobutyl aluminum, tri-n-hexyl aluminum,tri-octyl aluminum and the like. Of these, the more preferred are thecompounds having C₆ or higher alkyl groups which have better solubilityin the hydrocarbon solvent reaction medium. The aluminoxanes used toform the catalyst are preferably contained in organic solvents inconcentrations of from about 0.3 to 30 weight percent of total solventplus aluminoxane.

A trialkylaluminum compound can also be included in the catalyst (0.1 to1.0 mole per mole of aluminoxane).

The chromium complexes which, upon mixing with an aluminoxane, catalyzeethylene oligomerization, and especially trimerization in accordancewith the process of the invention, can be represented by the formula:LCrX_(n), wherein L is a coordinating polydentate phosphine, arsine orstibine ligand, and X represents anions which can be the same ordifferent and n is an integer of 2 to 4. Such complexes can be in theform of oligomers, i.e. (LCrX_(n))_(y), where y is 2 to 8. By"polydentate" is meant that the ligand contains multiple donor atoms forcoordination with chromium.

Preferred polydentate ligands include the following types:

(a) RY(R'ZR"R'")₂

wherein R, R" and R'" are hydrogen or C₁ to about C₂₀ hydrocarbyl andwhere R" and R'" can join to form a ring, especially a five-memberedring, which includes Z; R' is C₁ to about C₁₀ hydrocarbyl; and Y and Zare individually phosphorus, arsenic or antimony;

(b) CH₃ E(R'ZR"₂)₃

wherein E is C, Si, Ge or Sn and R', R" and Z are as defined in (a)above;

(c) E'(R'ZR"₂)₃

wherein E' is nitrogen, phosphorus, arsenic or antimony and R', R" and Zare as defined in (a) above; and

(d) A-ZR-B

wherein A is an integer of 9 to 18, B is an integer of 3 to 6, R is a C₁to C₁₀ alkyl group such as a methyl, ethyl, propyl, butyl, pentyl, hexylor higher allyl group or a C₆ to C20 aromatic group such as benzyl, andZ is phosphorous, arsenic or antimony. The abbreviations, such as9-PR-3, 10-PR-3, 12-PR4 and the like, used for the phosphine ligandscorrespond to those used for crown ethers because they are theirphosphorus analogues. For example, 9-PR-3 denotes a nine membered ringwith 3 equally spaced phosphorus atoms. The most preferred coordinatingpolydentate ligands of this type are facially coordinating tridentateligands, such as 9-PMe-3.

In the ligands of types (a), (b) and (c) each (R'ZR") moiety can bedifferent so as to provide a mixture of donors in the same complex. Theligands of types (a), (b), (c), and (d) can be modified to attach to apolyethylene chain (molecular wt.=1000 or higher) so that the resultingcatalyst is homogeneous (soluble) at elevated temperature but becomesheterogeneous (insoluble) at 25° C. This technique facilitates therecovery of the catalyst from the reaction products for reuse and hasbeen used with other catalysts as described, for example, by D. E.Bergbreiter et al., J. Chem. Soc., Chem. Commun., 337-338 (1985); J.Org. Chem. (1986) 51, 4752-4760; and J. Am. Chem. Soc. (1987), 109,177-179.

Non-limiting examples of specific tridentate phosphine ligands include:

for type (a), EtP(C₂ H₄ PEt₂)₂, whose chemical name isbis-(2-diethylphosphinoethyl)ethylphosphine;

for type (b), CH₃ C(CH₂ PEt₂)₃, whose chemical name is1,1,1-tris(diethylphosphinomethyl)ethane;

for type (c), P(C₂ H₄ PEt₂)₃, whose chemical name istris(2-diethylphosphinoethyl)phosphine; and

for type (d), 9-PMe-3, whose chemical name is1,4,7-trirethyl-1,4,7-triphosphinocyclononane.

Other specific examples are:

CH₃ C(CH₂ PPh₂)₃

PhP(CH₂ CH₂ PPh₂)₂

CyP(CH₂ CH₂ PCy₂)₂

PhP(CH₂ CH₂ PMe₂)₂

CyP(CH₂ CH₂ PMe₂)₂

CyP(CH₂ CH₂ PEt₂)₂

n-PrP(CH₂ CH₂ PEt₂)₂

EtP(C₃ H₆ PEt₂)₂

N(C₂ H₄ PEt)₃

PhP(o-C₆ H₄ PEt₂)₂

wherein Ph=phenyl, Cy=cyclohexyl, Me=methyl, Et=ethyl and Pr=propyl.

The arsine and stibine analogs of these ligands could also be prepared,for example:

PhAS(o-C₆ H₄ AsPh₂)₂

MeAs(o-C₆ H₄ AsMe₂)₂

MeSb(C₂ H₄ SbMe₂)₂

MeAs(C₃ H₆ AsMe₂)₂

Recent experimental results indicate that at least some compounds of theformula ##STR4## where each R is, independently, a hydrocarbyl group,such as MeP(C₃ H₆ PEt₂)₂ and PhP(C₃ H₆ PMe₂)₂, tend to form catalystswhich lose activity in relatively short periods of time.

The asymmetrical polydentate phosphines, arsines and stibines of thisinvention (formula (I) above) are exemplified by the following:

(2-dimethylphosphinoethyl)(3-dimethylphosphinopropyl)methylphosphine;

(2-dimethylphosphinoethyl)(3-dimethylphosphinopropyl)ethylphosphine;

(2-dimethylphosphinoethyl)(3-dimethylphosphinopropyl)butylphosphine;

(2-dimethylphosphinoethyl)(3-dimethylphosphinopropyl)octylphosphine;

(2-dimethylphosphinoethyl)(3-dimethylphosphinopropyl)dodecylphosphine;

(2-dimethylphosphinoethyl)(3-dimethylphosphinopropyl)cyclohexylphosphine;

(2-dimethylphosphinoethyl)(3-dimethylphosphinopropyl)cyclohexenylphosphine;

(2-dimethylphosphinoethyl)(3-dimethylphosphinopropyl)phenylphosphine;

(2-dimethylphosphinoethyl)(3-dimethylphosphinopropyl)p-tolylphosphine;

(2-dimethylphosphinoethyl)(3-dimethylphosphinopropyl)benzylphosphine;

(2-dimethylphosphinoethyl)(3-dimethylphosphinopropyl)phenethylphosphine;

(2-dimethylphosphinoethyl)(4-dimethylphosphinobutyl)methylphosphine;

(2-dimethylphosphinoethyl)(4-dimethylphosphinobutyl)ethylphosphine;

(2-dimethylphosphinoethyl)(4-dimethylphosphinobutyl)phenylphosphine;

(2-dimethylphosphinoethyl)(4-dimethylphosphinobutyl)cyclopentylphosphine;

(2-dimethylphosphinoethyl)(5-dimethylphosphinopentyl)methylphosphine;

(2-dimethylphosphinoethyl)(5-dimethylphosphinopentyl)phenylphosphine;

and the arsine and stibine analogs corresponding to these phosphines.

By a coordinating polydentate ligand is meant a ligand that stericallyencumbers the chromium atom in such a way that the rate of chainpropagation is decreased so that oligomerization, especiallytrmerization, rather than polymerization occurs. For example, ligandswhich occupy three adjacent coordination sites about an octahedralchromium atom.

Examples of suitable anions, X, include, but are not limited to, halides(Cl⁻, Br⁻, I⁻, F⁻), alkoxides (OR⁻), carboxylates (O₂ CR⁻), Oxo(O⁻²) andthe like. These anions are initially the anion portion of the chromiumcompounds used to make the complex. The chromium in the compounds isinitially in the oxidation state of II to VI and is preferably in theoxidation state of II, III or IV.

The known chromium complexes can be prepared according to procedures setforth in the literature. For example, L. R. Gray et al., J. Chem. Soc.Dalton. Trans. (1984), 47-53, A. M. Arif et al. Inorg. Chem., Vol. 25,No. 8, 1986, 1080-1084, and Diel et al., J. Am. Chem. Soc. 1982, 104,4700-4701. The synthesis of the novel asymmetrical ligands of thisinvention and chromium complexes thereof is illustrated in detail inExamples 12 through 15 hereinafter.

The chromium complex and aluminoxane are combined in proportions toprovide Al/Cr molar ratios of from about 1:1 to 10,000 to 1, preferablyfrom about 5:1 to 500 to 1. The amount of catalyst used is selected toprovide the desired reaction rates at any particular reaction scale.(The presence of amounts of about 0.001 mmole or more, preferably fromabout 0.1 to 10 mmoles of chromium catalyst in a 300 mL reactor, areeffective to catalyze the reaction.) Catalyst mixing is preferably doneat low temperatures of 0 to 35° C. The presence of ethylene duringcatalyst mixing at these temperatures resulted in no significantdifference in catalyst properties when compared with catalysts preparedin the absence of ethylene. Ethylene provided a protective effect attemperatures above 55° C.

The reaction with ethylene is carried out in an inert solvent. Any inertsolvent which does not react with aluminoxane can be used. The preferredsolvents are aliphatic and aromatic hydrocarbons and halogenatedhydrocarbons such as, for example, toluene, xylene, ethylbenzene,cumene, mesitylene, heptane, cyclohexane, methylcyclohexane, 1-hexene,1-octene, chlorobenzene, dichlorobenzene, and the like. The amount ofsolvent is not particularly critical and generally ranges from about 50to 99 wt. percent of the initial reaction mixture.

Reaction temperatures and pressures are chosen to optimize reactionrates and selectivity. In general temperatures of from about 35 to 200°C. are used and preferably 80 to 120° C. Temperatures in the range ofabout 35 to about 120° C. are particularly preferred, especially whenemploying catalysts in which the ligand is a compound of formula (I)above. Ethylene pressures can range from atmospheric to 3000 psigpreferably from about 100 to 1500 psig. Temperature and pressure affectreaction rate and purity in the following way: both higher temperatureand higher ethylene pressure increase reaction rate; higher ethylenepressures give better purity by forming less internal olefins, whereashigher temperatures increase the formation of internal olefins.

The trimerization catalysts described herein may be used in a process inwhich trimerization and polymerization of ethylene operatesimultaneously. One example of this type of process has been describedin E. A. Benham, P. D. Smith, and M. P. McDaniel, Polymer Engineeringand Science, 1988, 28, 1469.

The invention is lurrer illustrated by, but is not intended to belimited to, the following examples.

EXAMPLE 1 Preparation of Triphosphine Chromium Trichloride

Preparation of n-PrP(CH═CH₂)₂

To a 1.0 M solution of vinylMgBr (70 mmol) in THF at 0° C. was added asolution of n-PrPCl₂ (3.75 g, 25.9 mmol) in 35 mL THF over 1 hour. Thesolution was allowed to warm slowly and stirred overnight. To theresulting suspension was added degassed, saturated NH₄ Cl solution (50mL) slowly to kill the unreacted vinylMgBr. The organic phase wasseparated from the aqueous phase using a cannula. The remaining aqueousphase was washed with two 40-mL portions of Et₂ O, which were thencombined with the organic phase, dried over sodium carbonate anddistilled at ambient pressure under inert atmosphere to give 2.0 g (60%yield) of n-PrP(C₂ H₃)₂ (b.p.=143° C.).

Preparation of n-PrP(C₂ H₄ PEt₂)₂

A mixture of n-PrP(CH═CH₂)₂ (1.29 g, 10.0 mmol), Et₂ PH (2.25 g, 25.0mmol) and 2,2'-azobis(isobutyronitrile) (AIBN, 30 mg) in a closed flaskunder inert atmosphere was irradiated by a GE Sunlamp (275 W) one footaway for 24 hours. The resulting colorless liquid was stripped ofvolatiles under vacuum and vacuum distilled to give 3.1 g (97% yield) ofproduct collected at 132-135° C./0.35 mm Hg. ³¹ P-NMR (toluene): δ--18.5(2P); δ--22.8 (1P).

Preparation of [n-PrP(C₂ H₄ PEt₂)₂ ]CrCl₃

A mixture of n-PrP(C₂ H₄ PEt₂)₂ (2.30 g, 7.46 mmol) and anhydrous CrCl₃(0.40 g, 2.50 mmol) in a closed flask under vacuum was heated withstirring at 135° C. for 1 hour. The reaction mixture at this stagecontained four compounds: excess ligand (heptane-soluble), purple LCrCl₃(toluene-soluble), blue LCrCl₃ (CH₂ Cl₂ -soluble), and unreacted CrCl₃.Separation was achieved by solubility difference. The resulting bluecake was extracted with 20 mL of toluene, filtered, and washed withtoluene until colorless. Toluene was removed from the combined purplefiltrate, the residue was extracted with heptane, filtered to give apurple solid and unreacted ligand in beptane. The insoluble materialswere a mixture of a blue solid and unreacted CrCl₃. Separation wasachieved by extraction with CH₂ Cl₂. Unreacted CrCl₃ (0.05 g) wasrecovered. Results: blue solid; 0.65 g, purple solid; 0.35 g. Thecombined yield was quantitative based on reacted CrCl₃. The blue andpurple solids are both active in the ethylene trimerization reaction.Analysis for the blue compound, Calculated: P, 19.91; Cl, 22.79; Cr,11.14; C, 38.60; H, 7.56. Found: P, 19.77; Cl, 23.14; Cr, 11.46; C,38.20; H 7.65.

The following diagram shows the X-ray crystal structure of the purpleproduct: ##STR5##

Another ligand-hromium complex, [CyP(C₂ H₄ PEt₂)₂ ]CrCl₃, where Cy iscyclohexyl, was prepared analogously.

EXAMPLE 2 Ethylene Tinerization Reaction

The reaction was carried out in a 300 mL Parr stainless-steel reactor towhich a liquid addition bomb was connected for the purpose of adding thealuminonne solution under ethylene pressure. To the reactor containing asolution of [n-PrP(C₂ H₄ PEt₂)₂ ]CrCl₃ (blue compound, 45 mg, 0.096mmol) and pentadecane (0.267 g, as internal reference for gaschromatography) in 90 mL of toluene at 25° C. under 250 psig of ethylenepressure was added a solution of n-hexylaluminoxane (5.0 mmol) in 10 mLof toluene using ethylene gas which brought the pressure to 300 psig.The chain-growth reaction was then carried out with continuous ethylenefeed at 95° C./610 psig for one hour (strring rate: 800 RPM), duringwhich time 22 g of ethylene was consumed. The reaction was terminated bypressing methanol into the reactor to deactivate the catalyst. Thereactor was cooled to 10° C., vented, and a sample was withdrawn for GCanalysis which showed the following results: C₄ : 4.3%, C₆ : 94.3%,C_(8:) 0.2 %, C₁₀ : 0.9%. The polymer produced was only 0.1% and thepurity of 1-hexene was 92.6% with major impurities being internalhexenes. The weights of the carbon fractions were calculated usingmeasured response factors and minic experiments to simulate theoperational loss of light olefins.

Results of this and other Examples 3-11 with varied reaction conditionsare summarized in Table I. Except for Example 11, only small amounts ofpolyethylene were formed in the process and the butene co-product rangedfrom about 3 to 15 percent. Hexene production was at least 80%,Impurities in the complex can cause increased polymer formation, as perExample 11, such that if such polymer formation occurs, the purity ofthe complex should be checked. The process, by avoiding significantamounts of polyethylene, has the advantages that the reactions in acommercial operation would not require frequent cleaning, as would bethe case with the prior art processes and also the catalyst life isextended. For example a catalyst of n-PrP(C₂ H₄ PEt₂)₂ CrCl₃retains >90% of its initial activity even after 12 hours of reaction,giving a catalyst productivity of about 8000 g hexene/g Cr catalystcompound. The catalysts according to the prior art gave catalystproductivities in the range of only 500-1,000.

                                      TABLE I                                     __________________________________________________________________________    Catalyzed Ethylene Trimerization Reactions.sup.1                                   Catalyst             Distribution                                                                              Purity                                  Example                                                                            (mmol).sup.2                                                                        Pressure                                                                          Temperature                                                                              (wt. %)     (wt. %)                                                                            Polymer                            No.  Cr Al (psig)                                                                            (°C.)                                                                        Activity.sup.3                                                                     C.sub.4                                                                          C.sub.6                                                                          C.sub.8                                                                          C.sub.10                                                                         1-hexene                                                                           (wt. %)                            __________________________________________________________________________    3    .096                                                                             5.0                                                                              610 95    8,200                                                                              4.1                                                                              94.3                                                                             .17                                                                              .64                                                                              92.6 0.6                                4    .100                                                                             5.0                                                                              620 80    3,200                                                                              3.1                                                                              94.4                                                                             .23                                                                              .52                                                                              94.4 1.5                                5    .096                                                                             5.0                                                                              700 115   11,100                                                                             9.6                                                                              89.3                                                                             .20                                                                              .65                                                                              87.4 0                                  6    .088                                                                             5.0                                                                              970 94    17,000                                                                             3.2                                                                              94.9                                                                             .11                                                                              .59                                                                              93.7 1.1                                7    .084                                                                             5.0                                                                              960 85    11,700                                                                             2.3                                                                              96.4                                                                             0.1                                                                              0.6                                                                              95.0 0.4                                8    .069                                                                             5.0                                                                              610 106   7,800                                                                              8.6                                                                              90.3                                                                             .23                                                                              .62                                                                              90.0 0.1                                (purple [n-PrP(C.sub.2 H.sub.4 PEt.sub.2).sub.2 ]CrCl.sub.3                   9    .084                                                                             6.0                                                                              610 94    5,700                                                                              15.0                                                                             83.0                                                                             .13                                                                              .42                                                                              91.9 1.3                                (propylaluminoxane was used)                                                  10   .097                                                                             10.0                                                                             630 95    14,000                                                                             10.5                                                                             88.7                                                                             .38                                                                              .26                                                                              90.2 0.1                                (blue [CyP(C.sub.2 H.sub.4 PEt.sub.2).sub.2 ]CrCl.sub.3 and                   butylaluminoxane were used)                                                   11.sup.4                                                                           .071                                                                             5.0                                                                              590 94    7,900                                                                              4.5                                                                              82.0                                                                             0.8                                                                              0.5                                                                              93.2 12.0                               __________________________________________________________________________     .sup.1 Reactions were carried out in 100 mL toluene for one hour.             .sup.2 Hexylaluminoxane and blue [nPrP(C.sub.2 H.sub.4 PEt.sub.2).sub.2       ]CrCl.sub.3 were used unless otherwise noted.                                 .sup.3 Activity = mol ethylene/mol Cr/hr.                                     .sup.4 A less pure complex was used, prepared from CrCl.sub.3 THF.sub.3,      which resulted in a high amount of polymer coproduct.                    

Comparison 1

The triphosphine ligand, n-PrP(C₂ H₄ PEt₂)₂ was used as part of a threecomponent CrX₃ /aluminoxane/ligand system, where X is 2-ethylhexanoate(a mixed system as suggested in Briggs, U.S. Pat. No. 4,668,838, asopposed to a preformed chromium complex as per the process of theinvention) A low yield of impure 1-hexene was formed along with asimilar amount of undesirable polyethylene. The main product was butenes(72%). According to the process a mixture of n-PrP(C₂ H₄ PEt₂)₂ (62 mg,0.2 mmol) in toluene and Cr(2-ethylhexanoate)₃ in heptane (10% solution,0.48 g solution, 0.1 mmol Cr) was allowed to react for 10 minutes withstirring in a dry box. To it was added isobutylaluminoxane (6.0 mmol) intoluene. The total amount of toluene was about 100 mL, and 115 mg ofpentadecane was added as an internal reference for gas chromatography.The above mixture was transferred to a 300 mL Parr reactor, sealed, andpressured with 25 g. of ethylene (33° C./415 psig). The reaction washeated to 92-105° C. and ethylene pressure dropped from 680 psig to 390psig over 8 minutes. After cooling, unreacted ethylene was vented at 31°C. (230 psig). The product contained 1.2 grams of polymer (12%), 1.5grams of hexenes (15%, purity 90.9%) and 7.0 grams of butenes (72%,purity 88.6% and a trace of C₈ and higher materials). The results showthat using a tridentate ligand as a third component, as opposed to apreformed complex with chromium, not only caused a loss of trimerizationactivity, but 12% polymer formation occurred. Also, a lower vinyl purityresulted. Note that this reaction used excess (2:1) ligand. Even morepolymer would be expected to form if less ligand is used, based on theresults obtained when using the previous 9-NMe-3 ligand.

Comparison 2

A mixture of n-PrP(C₂ H₄ PEt₂)₂ (62 mg, 0.2 mmol), anhydrous CrCl₃ (23mg, 0.15 mmol) isobutylaluminoxane (5.3 g solution, 6.0 mmol), andpentadecane (68 mg) in about 100 mL of toluene, was stirred at roomtemperature in a dry box for 10 minutes. No dissolution of CrCl₃ wasobserved. The mixture was poured into a Parr (300 nL) reactor, sealed,pressurized with 25 g of ethylene and heated to 96° C. The pressure was725 psig. Because no pressure drop was observed after 17 minutes underthese conditions, the temperature was brought to 125° C. As soon as thetemperature reached 120° C. (800 psig) ethylene consumption took place.Within 5 minutes the pressure dropped from 800 to 160 psig at 120-128°C. The reactor was cooled without quenching the catalyst and unreactedethylene was released at 30° C. The solution was light purple with about2/3 of the CrCl₃ remaining unreacted. The product by GC contained 90%butenes (76.4% pure), 9% hexene (74.2% pure) and a trace of polymer. Theresults show that a poor yield of impure C₆ was produced and, althoughonly a trace of polymer was found, the major product was butenes.

The following non-limiting examples illustrate the exceptional resultsachievable by producing and using the asymmetrical tridentate phosphine,arsine or stibine compounds of this invention.

EXAMPLE 12 Preparation of(2-Dimethylphosphinoethyl)(3-dimethylphosphinopropyl)phenylphosphine

A. Preparation of Me₂ PCH₂ CH═CH₂

Using solvents degassed with nitrogen and conducting the operationsunder dry nitrogen, allyldimethylphosphine was formed by reactingdimethylchlorophosphine with allylmagnesium bromide as follows: To aclear solution of 140 mmol of allylmagnesium bromide in tetrahydrofuran(THF) was added 100 mL of diglyme, and THF was stripped from the mixtureunder vacuum at 25° C. until the boiling visibly slowed down. To theresulting thick, dark gray suspension in a flask wrapped in aluminumfoil was added dropwise over a 50-minute period, a mixture of 108 mmolof dimethylchlorophosphine in 8 grams of diglyme. An external water bathwas used to maintain the temperature of the exothermic reaction below35° C. The reaction mixture was stirred overnight. The suspension wasvacuum distilled at 25° C. under vacuum using a liquid nitrogen trap.The distillation was terminated when the boiling visibly slowed down. Anear quantitative yield of product (42.33 grams) as a cloudy solutionwas collected and redistilled at atmospheric pressure and 16 grams of acloudy solution was recovered between 70 and 150° C. GC showed thepresence of 70.8% of allyldimethylphosphine. ³¹ P-NMR showed only onepeak at -52.5 ppm, indicating the absence of oxides and the absence ofdimethylchlorophosphine.

B. Preparation of Me₂ PCH═CH₂

To form dirnethylvinylphosphine, the reaction ofdiinethylchlorophosphine with vinylmagnesium bromide was conducted inessentially the same manner as the above synthesis ofallyldimethylphosphine. In particular, 100 mL of diglyme was added to100 mL of a 1.0 molar solution of vinylmagnesium bromide in THF. Theorange-brown solution was stripped under vacuum until more than 95% ofthe THF was removed. A mixture of 77.4 mmol of dimethylchlorophosphinein 8 grams of diglyme was added dropwise over a 25-minute period to theyellow suspension of the vinyl Grignard reagent in a flask wrapped inaluminum foil. The reaction mixture was kept at about room temperatureand stirred overnight. The product solution was subjected to a lowvacuum and volatiles stripped into a flask externally cooled by liquidnitrogen. The colorless product solution was found to contain 39.4% ofdimethylvinylphosphine, and the product was formed in near quantitativeyield. ³¹ P-NMR showed the product to have a single peak at -48.7 ppm.

C. Preparation of PhP(M)(C₃ H₆ PMe₂)

To produce (3-dimethylphosphinopropyl)phenylphosphine a mixture of(allyl)PMe₂ (20.8 mmol), PHPH₂ (35.3 mmol), and2,2'-azobis(isobutyronitrile) (AIBN, 0.2 g) in a 16° C. water bath withstirring was irradiated by a 275W sunlamp from ca. 20 cm away under N₂.After two days of irradiation, a 4:1 by weight mixture of PhP(H)(C₃ H₆PMe₂) and PhP(C₃ H₆ PMe₂)₂ was obtained, along with excess PhPH₂. Themixture was vacuum-distilled using a 15 cm Vigreux condenser. Thedesired diphosphine was collected at 68-71° C./0.03 mm Hg: 12.7 mmol,61% isolated yield. GC showed that it is contaminated by only a trace ofPhPH₂ and ca. 0.4% of the triphosphine. ³¹ p-NMR (toluene-d₈): -52.8 ppm(s, P-Me) and -53.5 ppm (s, P-Ph).

D. Preparation of PhP(C₂ H₄ PMe₂)(C₃ H₆ PMe₂)

A mixture of PhP(H)(C₃ H₆ PMe₂) (12.7 mmol), (vinyl)PMe₂ (19 mmol), andAIBN (0.2g) in a 16° C. water bath with stirring was irradiated by a275W sunlamp from ca. 20 cm away under N₂. After two days ofirradiation, the resulting light yellow liquid was stripped of volatilesunder vacuum at temperatures up to 90° C. The residue was flashdistilled at 170° C./0.03 mm Hg to give(2-dimethylphosphinoethyl)(3-dimethylphosphinopropyl)phenylphosphine asa pale yellow liquid (11.9 mmol, 93% isolated yield). GC again showedthe presence of ca. 0.4% of PhP(C₃ H₆ PMe₂)₂. ³¹ P-NMR (toluene-d₈)revealed: -21.7 ppm (d, 23 Hz, P-Ph), -47.8 ppm (d, 23 Hz, P-C2), and-53.5 ppm (s, P-C3). Mass m/z (relative intensity): 300(4,[M⁺ ]), 285(11, M-CH₃), 211 (100, M-C₂ H₄ PMe₂), 197 (6, M-C₃ H₆ PMe₂).

EXAMPLE 13 Preparation of(2-Dimethylphosphinoethyl)(3-dimethylphosphinopropyl)phenylphosphineComplex of Chromium Trichloride

A stirred mixture of ligand(2-dimethylphosphinoethyl)(3-dimethylphosphinopropyl)phenylphosphine(11.8 mmol) and anhydrous CrCl₃ (3.2 mmol) was heated at 173° C. forthree hours. To the resulting purple cake after cooling was addedheptane (22 g) and the suspension was filtered to separate the excessligand. The purple solid contaminated with ca. 3-5% unreacted CrCl₃ waspurified by dissolving in CH₂ Cl₂ (17.6 g), filtering into heptane (26g), stripping off most of the CH₂ Cl₂ under vacuum, and again filteringto give the desired complex, [PhP(C₂ H₄ PMe₂)(C₃ H₆ PMe₂)]CrCl₃, as apurple-brown powder (2.9 mmol, 91% yield). Elemental analysis:Calculated: C: 39.32%, H: 5.96%, Cr.: 12.01%; Found: C: 39.28%, H:5.93%, Cr.: 11.34%.

EXAMPLE 14 Preparation of(2-Diethylphosphinoethyl)(3-diethylphosphinopropyl)cyclohexylphosphine

CyP(C₂ H₄ PEt₂)(C₃ H₆ PEt₂), distillable at 167-169° C. at 0.07 mm Hg,was prepared from CyPH₂, (vinyl)PEt₂, and (allyl)PEt₂ using proceduresanalogous to those of Example 12 above. Analysis by ³¹ P-NMR(toluene-d₈) revealed: -15.3 ppm (d, 19.3 Hz, P-Cy), -18.8 ppm (d, 19.3Hz, P-C2), and -24.7 ppm (s, P-C3). Mass m/z (relative intensity):362(2,[M⁺ ]), 333 (60, M-Et), 279 (100, M-C₆ H₁₃), 245 (26, M-C₂ H₄PEt₂).

EXAMPLE 15 Preparation of(2-Diethylphosphinoethyl)(3-diethylphosphinopropyl)cyclohexylphosphineComplex of Chromium Tricloride

The desired complex was prepared in 78% yield by reacting CyP(C₂ H₄PEt₂)(C₃ H₆ PEt₂) prepared as in Example 14 with CrCl₃ at 162° C. forthree hours. Elemental analysis revealed: Calculated: C: 43.27%, H:7.78%, Cr: 11.42%; Found: C: 43.82%, H: 7.93%, Cr.: 9.98%.

EXAMPLES 16-23 Ethylene Trimerization Reaction

Using procedures analogous to those of Example 2 above, additionalcatalysts were formed from the chromium trichloride complexes ofExamples 13 and 15 above--both of which were based on use ofunsymmetrical tridentate phosphine ligands--and a butylaluminoxane. Bothcatalysts showed activity in producing 1-hexene. However, the catalystformed by use of a novel ligand of this invention, namely,(2-dimethylphosphinoethyl)(3-dimethylphosphinopropyl)phenylphosphinegave excellent results as compared to the catalyst based on(2-diethylphosphinoethyl)(3-diethylphosphinopropyl)cyclohexylphosphine,a triphosphine compound which, per se, is not a triphosphine of thisinvention. These results are summarized in Table 2 (cf. Examples 16-20versus Example 21). Table 2 also presents results recently obtainedusing other analogous catalysts.

                                      TABLE 2                                     __________________________________________________________________________    Catalyzed Ethylene Trimerization Reactions.sup.1                                   Catalyst             Distribution                                                                              Purity                                  Example                                                                            (mmol).sup.2                                                                        Pressure                                                                          Temperature                                                                              (wt. %)     (wt. %)                                                                            Polymer                            No.  Cr Al (psig)                                                                            (°C.)                                                                        Activity.sup.3                                                                     C.sub.4                                                                          C.sub.6                                                                          C.sub.8                                                                          C.sub.10                                                                         1-hexene                                                                           (wt. %)                            __________________________________________________________________________    16.sup.2                                                                           .20                                                                              10.0                                                                             230 88    17,000                                                                             2.6                                                                              95.2                                                                             -- 2.2                                                                              98.0 None                               17.sup.2                                                                           .028                                                                             6.0                                                                              610 80    63,000                                                                             1.0                                                                              97.7                                                                             -- 1.0                                                                              98.8  0.30                              18.sup.2                                                                           .027                                                                             6.0                                                                              510 60    48,700                                                                             0.92                                                                             98.3                                                                             --  0.45                                                                            99.0  0.33                              19.sup.2                                                                           .026                                                                             6.0                                                                              520 60    27,200                                                                             0.75                                                                             96.3                                                                             -- 1.2                                                                              98.9 1.8                                20.sup.2                                                                           .028                                                                             6.0                                                                              520 60    --.sup.4                                                                           0.64                                                                             97.6                                                                             --  0.96                                                                            99.0  0.78                              21   .20                                                                              12.0                                                                             610 86      440                                                                              53.4                                                                             43.8                                                                             -- -- 95.2 2.7                                Ligand was CyP(C.sub.2 H.sub.4 PEt.sub.2)(C.sub.3 H.sub.6 PEt.sub.2)          22   .20                                                                              12.0                                                                             580 87    .sup. 20,000.sup.5                                                                 20.0                                                                             74.6                                                                             -- -- 93.5 5.3                                Ligand was MeP(C.sub.3 H.sub.6 PEt.sub.2).sub.2                               23   .10                                                                              6.0                                                                              600 85    .sup. 40,000.sup.6                                                                 2.6                                                                              95.0                                                                             --  0.08                                                                            98.7 1.7                                Ligand was PhP(C.sub.3 H.sub.6 PMe.sub.2).sub.2                               __________________________________________________________________________     .sup.1 Reaction solvent was toluene except Ex. 19 which used heptane; the     aluminoxanes were either nbutyl or isobutylaluminoxane.                       .sup.2 Catalyst was based on a ligand of this invention, viz., PhP(C.sub.     H.sub.4 PMe.sub.2)(C.sub.3 H.sub.6 PMe.sub.2); see Example 12D.               .sup.3 Activity = mol ethylene/mol Cr/hr.                                     .sup.4 Activity was 60,000 to 34,000 for 1 hr & 50 min; 28,000 to 25,000      for 2 hr & 48 min; & 23,000 to 21,000 for 3 hr & 36 min.                      .sup.5 Reaction lasted for less than 3 minutes at which point the catalys     lost its activity.                                                            .sup.6 Reaction lasted for 15 minutes at which point the catalyst lost it     activity.                                                                

In Example 17 the activity of the catalyst went from 160,000 to 30,000in a 48-minute period during which time the productivity of the catalystwas 3,100 grams of olefin per gram of ligand-chromium complex. InExample 18 the activity of the catalyst went from 70,000 to 40,000 in a45-minute period. The activity of the catalyst of Example 19 went from37,000 to 26,000 during the first hour and remained at 26,000 over thenext two hours. In this three-hour period the productivity of thecatalyst was 5,500 grams of olefm per gram of ligand-chromium complex.The catalyst of Example 20 had a productivity over an 8-hour period of14,000 grams of olefm per gram of ligand-chromium complex. It can beseen therefore that the ligand of formula (I) above formed anexceptionally effective catalyst.

Examples 24-32 further illustrate and define various embodiments of thecatalyst compositions of this invention.

EXAMPLE 24

This example shows an ethylene trimerization catalyst compositioncomprising an aluminoxane and a polydentate phosphine, arsenic and/orstibine coordination complex of a chromium salt, wherein the mole ratioof aluminum to chromium in the catalyst is in the range of from about1:1 to about 10,000:1; wherein said complex has the formula LCrX_(n),where L is a coordinating polydentate phosphine, arsine and/or stibineligand, X represents anions which can be the same or different, and n isan integer of 2 to 4; and wherein said ligand has the formula ##STR6##where Z, which can be the same or different, is phosphorus, arsenic orantimony, R is a hydrocarbyl group, R¹ is a dimethylene group and R² isa linear polymethylene group having at least 3 carbon atoms.

EXAMPLE 25

This example shows a composition according to Example 24 wherein Z isphosphorus.

EXAMPLE 26

A composition according to Example 24 wherein R² is a lineartrimethylene group.

EXAMPLE 27

This example shows a composition according to Example 26 wherein Z isphosphorus.

EXAMPLE 28

This example shows a composition according to Example 27 wherein X is ahalide anion and n is 3.

EXAMPLE 29

A composition according to Example 24 wherein the mole ratio of aluminumto chromium in the catalyst is in the range of from about 5:1 to about500:1.

EXAMPLE 30

This example shows a composition according to Example 29 wherein Z isphosphorus and R² is a linear trimethylene group.

EXAMPLE 31

This example shows a composition according to Example 29 wherein saidligand is(2-dimethylphosphinoethyl)(3-dimethylphosphinopropyl)phenylphosphine.

EXAMPLE 32

This example shows a composition according to Example 29 wherein saidchromium salt is a chromium trihalide and said ligand is a(2-dimethylphosphinoethyl)(3-dimethylphosphinopropyl)hydrocarbylphosphine.

This invention is susceptible to considerable variation in its practice.Therefore the foregoing description is not intended to limit, and shouldnot be construed as limiting, the invention to the particularexemplifications presented hereinabove. Rather, what is intended to becovered is as set forth in the ensuing claims and the equivalentsthereof permitted as a matter of law.

What is claimed is:
 1. A polydentate phosphine, arsenic and/or stibinecoordination complex of a chromium salt having the formula LCrX_(n),where L is a coordinating polydentate phosphine, arsine and/or stibineligand, X represents anions which can be the same or different, and n isan integer of 2 to 4; and wherein said ligand has the formula ##STR7##where Z can be the same or different and is phosphorus, arsenic orantimony, R is a hydrocarbyl group, R¹ is a dimethylene group and R² isa linear polymethylene group having at least 3 carbon atoms.
 2. Acomplex according to claim 1 wherein Z is phosphorus and R² is a lineartrimethylene group.
 3. A complex according to claim 1 wherein saidchromium salt is a chromium trihalide and said ligand is a(2-dimethylphosphinoethyl)(3-dimethylphosphinopropyl)hydrocarbylphosphine.4. An ethylene trimerization catalyst composition comprising analminoxane and a polydentate phosphine, arsenic and/or stibinecoordination complex of a chromium salt, wherein the mole ratio ofaluminum to chromium in the catalyst is in the range of from about 1:1to about 10,000:1; wherein said complex has the formula LCrX_(n), whereL is a coordinating polydentate phosphine, arsine and/or stibine ligand,X represents anions which can be the same or different, and n is aninteger of 2 to 4; and wherein said ligand has the formula ##STR8##where Z can be the same or different and is phosphorus, arsenic orantimony, R is a hydrocarbyl, group, R¹ is a dimethylene group and R² isa linear polymethylene group having at least 3 carbon atoms.